Spatial Fitting by Percept Location Tracking

ABSTRACT

The present invention is an improved spatial fitting and training system for a visual prosthesis. The system of the present invention maps projected locations of percepts, where a person perceives a percept from a visual prosthesis to the intended location of the percepts. The projected location may vary over time. These test results can be used to correct a visual prosthesis or spatially map the visual prosthesis.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a divisional application of U.S. patentapplication Ser. No. 15/144,616, filed May 2, 2016, for Spatial Fittingby Percept Location Tracking, which claims priority to U.S. ProvisionalPatent Application 62/156,119, filed May 1, 2015, for Spatial Fitting byPercept Location Tracking.

FIELD

The present disclosure relates to visual prostheses configured toprovide neural stimulation for the creation of artificial vision, andmore specifically, an improved system for fitting and training for avisual prosthesis.

BACKGROUND

Applicants have developed many methodologies for fitting an electrodearray to a patient including: U.S. Pat. No. 8,271,091, for Visualprosthesis fitting; U.S. Pat. No. 8,195,301 Video configuration fileeditor for visual prosthesis fitting and related method; U.S. Pat. No.8,190,267, for Fitting a neural prosthesis using impedance and electrodeheight; U.S. Pat. No. 8,180,454, for Fitting a neural prosthesis usingimpedance and electrode height; U.S. Pat. No. 7,908,011, for Visualprosthesis fitting; U.S. Pat. No. 7,818,064, for Fitting of brightnessin a visual prosthesis; U.S. Pat. No. 7,738,962, for Fitting ofbrightness in a visual prosthesis; U.S. Pat. No. 7,493,169 for Automaticfitting for a visual prosthesis; U.S. Pat. No. 7,483,751, for Automaticfitting for a visual prosthesis. The preceding list includes both manualand automated fitting methods. Both have advantages and disadvantages.What is needed is a method that uses the best advantages of both manualand automatic fitting.

SUMMARY

The present invention is an improved spatial fitting and training systemfor a visual prosthesis. The system of the present invention mapsprojected locations of percepts (PLP), where a person perceives apercept from a visual prosthesis, to the intended location of thepercepts. The projected location may vary over time. These test resultscan be used to correct a visual prosthesis or spatially map the visualprosthesis. While a patient can be initially fitted on a purely spatialbasis, by correcting for the error of each PLP in a single session,understanding the change in PLP over time provides for a more accuratefit of the patient.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a diagram of a subject using the touch screen monitor toindicate the projected location of perception.

FIG. 2 shows the change in PLP over time for a first subject.

FIG. 3 shows the change in PLP over time for a second subject.

FIG. 4 shows the change in PLP over time for a third subject.

FIG. 5 shows the horizontal change in PLP over time for a first subject.

FIG. 6 shows the horizontal change in PLP over time for a secondsubject.

FIG. 7 shows the horizontal change in PLP over time for a third subject.

FIG. 8 shows the vertical change in PLP over time for a first subject.

FIG. 9 shows the vertical change in PLP over time for a second subject.

FIG. 10 shows the vertical change in PLP over time for a third subject.

FIG. 11 shows the reduction in error centroid distances over time.

FIG. 12A shows relative increases in localization errors when nofeedback was provided for S1. FIG. 12B shows relative increases inlocalization errors when no feedback was provided for S2. FIG. 12C showsrelative increases in localization errors when no feedback was providedfor S3.

FIGS. 13 and 14 show a video capture/transmission apparatus or visoradapted to be used in combination with the retinal stimulation of FIGS.22 and 23.

FIG. 15 shows components of a fitting system according to the presentdisclosure, the system also comprising the visor shown in FIGS. 13 and14.

FIG. 16 shows the external portion of the visual prosthesis apparatus ina stand-alone mode, i.e. comprising the visor connected to a videoprocessing unit.

FIGS. 17-18 show the video processing unit in more detail alreadybriefly shown with reference to FIGS. 15 and 16.

FIG. 19A shows a LOSS OF SYNC mode.

FIG. 19B shows an exemplary block diagram of the steps taken when VPUdoes not receive back telemetry from the Retinal stimulation system.

FIG. 19C shows an exemplary block diagram of the steps taken when thesubject is not wearing glasses.

FIGS. 20-1, 20-2, 20-3 and 20-4 show an exemplary embodiment of a videoprocessing unit. FIG. 20-1 should be viewed at the left of FIG. 20-2.FIG. 20-3 should be viewed at the left of FIG. 20-4. FIGS. 20-1 and 20-2should be viewed on top of FIGS. 20-3 and 20-4.

FIG. 21 is flow chart of the video processing chain in a visualprosthesis.

FIG. 22 is a perspective view of the implanted portion of the preferredvisual prosthesis.

FIG. 23 is a side view of the implanted portion of the preferred visualprosthesis showing the fan tail in more detail.

FIG. 24 is a view of the completed package attached to an electrodearray.

FIG. 25 is a cross-section of the package.

DETAILED DESCRIPTION

The present invention is an improved spatial fitting and training systemfor a visual prosthesis. The system of the present invention mapsprojected locations of percepts, where a person perceives a percept froma visual prosthesis, to the intended location of the percepts. Theprojected location may vary over time. This test results can be used tocorrect a visual prosthesis or spatially map the visual prosthesis.

FIG. 1 shows a subject being fitting by the method of the presentinvention. The subject looks at a touch screen monitor 1 using thevisual prosthesis via the visual prosthesis camera 7. A square ispresented on the touch screen monitor 1 at the true location 6. Thesubject indicates the perceived location of percept (PLP) 4.

Subjects: 3 end-stage RP patients implanted with the Argus® IIepiretinal prosthesis.

Experiment: Participants attempted to touch a white square target on ablack background on a touchscreen monitor 1. Touchscreen dimensions:37.5 cm×30 cm (˜54°×44° of visual field).

Touchscreen resolution: 1024×768 pixels

Approximate camera-to-screen distance: 37 cm

Typical target size: 3 cm×3 cm (˜4°×4° of visual field)

Typical number of trials (targets to touch) per trial run: 40

Trial runs per testing session (mean±SD): 6.0±7.7 (range=1-30)

Camera sampling position (CSP): position of the approximate17.23°×10.21° area sampled for prosthesis processing out of the 66°×49°area captured by the prosthesis camera. CSPs were adjusted to reduceerrors when necessary. PLPs were tracked over periods ranging 154-959days.

Computer software recorded the location of each target and subjectresponses. Errors, in degrees of visual field, were calculated for eachresponse. Errors were combined with CSPs to estimate PLPs for eachtrial. Trial PLPs were averaged within trial runs. 95% confidenceintervals (CIs) were established for trial run PLPs based ont-distributions. To reduce bias introduced by CSPs, only trial run PLPsthat contained their corresponding CSPs within their CIs, and that hadwithin-subject smaller-than-average CIs, were considered for analysis.

Significance of horizontal (FIGS. 5-7) and vertical (FIGS. 8-10)differences in PLPs for individual subjects across trial runs wasevaluated using a bootstrap variation of ANOVA. Only PLP measurementswith non-intersecting confidence intervals were considered forcalculating rates of significant change. Data compilation, statisticalcalculations, and plots were produced using R 3.1.3.

There was a significant effect of trial run (i.e. differences acrosstime) on both horizontal and vertical components of PLPs for all threesubjects (p<10⁻⁴), not discernibly linked to any external parameters.

Within-subject ranges of fluctuation of PLP components: Range: 6.7°-25°

Mean=16°

Standard deviation (SD)=6.8°.

Rates of significant change for PLP components:

Range: 1.3°/year-4.4°/hour

Mean=5.9°/day

Median=0.13°/day

SD=24°/day

No measured PLPs displayed long-term stability.

PLPs displayed a lack of long-term stability in all three subjects.

Periods of short-term stability were broken by shifts as dramatic as upto 4.4°/hour.Rates of PLP change were highly variable, with a standard deviation of24°/day. While we do not know precisely what causes these fluctuations,continuing research suggests eye movement patterns during stimulationmight play a large role. As prosthesis subjects with constant correctivefeedback display much slower rates of adaptation to inaccurate CSPs, andno adaptation without corrective feedback, regular recalibrations ofprosthesis CPs are required to maintain subject hand-cameracoordination. Feedback can come in multiple forms from a simply right orwrong indication to a detailed direction and distance correction.

FIGS. 2-4 shows PLP estimates for three subjects, one subject eachfigure. The three subjects are denoted by descriptors S1, S2 and S3 topreserve patient privacy. PLP estimates from trial runs with S1 thatsimultaneously satisfied CI requirements in both horizontal and verticaldirections. Error bars indicate 95% confidence intervals. Arrowsindicate chronological order.

FIGS. 5-10 show the PLP estimates separated for horizontal and verticalcomponents. These plots separate horizontal and vertical PLP componentsfor each subject, displayed against their dates of measurement. Errorbars indicate 95% confidence intervals for each point, based on theircorresponding trial runs.

Square or Circle Localization:

In the Square Localization test, a high-contrast white square (80×80pixels, or 3 cm×3 cm) was presented in random locations on a 20″ touchscreen monitor 1 in front of the subject. When prompted, the subjectscanned the monitor and located the square, touching the screen at thelocation of the square center. Subjects first completed a short practicerun (10-trial), in which they selected the location of the square bytouching the monitor where they wanted it to appear. Next, a 40-trialtest was administered. No feedback was given to the subject during thetest.

Mean errors from the square localization assessment can be used toadjust the field of view the camera presents to the electrode array.This can be done by physically moving the camera angle with respect tothe glasses or translating the camera position with respect to theglasses. This can also be done electronically by selecting theappropriate field of view from the camera signal to feed to the implant.Because the image captured by the camera and stored in memory is muchlarger than the field of view associated with the electrode array on theretina, electronic control can be accomplished by down-selecting anappropriate window of video data from the image. Refer to “Video Windowoffset Setting” with respect to FIG. 21.

Further, another shape, such as circle or square, with an intensity thatis brightest at the center that gradually fades out, may reduce edgeeffects and measurement error. The size of the shape could be set to theminimum the size that is detectable by the subject, further reducing themeasurement error.

The x (horizontal) and y (vertical) location of the error centroid ofthe square localization assessment gives you the apparent location thatthe patient believes the percepts are appearing on average relative tothe current camera alignment position. By correcting for this offsetwith camera position or field of view position, the patient'sperceptions can be aligned with visual stimuli from the monitor. Forexample, if the error centroid was 1 degree to the right of the expectedcenter location, the camera could be angled to the right by 1 degree (orthe field of interest could be electronically moved to the right by 1degree). This, of course, works in the vertical direction too.

It has been noted elsewhere that even sighted subjects have a largedegree in of error in tasks of this type when they are not able to seetheir hand as they proceed to point to a target. There are otheranalyses besides mean and standard deviation that may be moreadvantageous. For instance, cluster analysis of the data would behelpful when the points fall into more than one region. A momentanalysis (center of mass) approach where the pixels were weighted wouldalso improve the precision of the point.

Further, it is also likely that the sources of error sum to locationswith a probability density function that is not Gaussian, but rathercould have several modes, and it is unlikely that the statistics of therandom variables that characterize the measurement error are stationarywithin an electrode and ergodic over the ensemble of all of theelectrodes. Thus non Gaussian distributions can be used to estimate thelocation of perception. This can include but is not limited to Binomial,Poison with parameter, Geometric with parameter, negative binomial withparameters, and Gamma with parameters. These distribution functions areknown in the context of estimation, stochastics, and thecharacterization of random variables. In the case where the measurementerrors are mixed, there will be a central location that is close to thetrue measurements, and overlapping data from probability distributionsof the various error sources. In this case, minimum error classificationcan be used to select the most likely target to use when adjusting thecamera. There are several types of appropriate minimum errorclassification methods that are known in the art.

A variant on the method discussed above is to make many measurements atone stimulation location and then use the estimated location tophysically or electronically move the camera toward this location. Thiscould be done with several other stimulation locations until thedifference between the stimulation location and the presented squareconverge to within an acceptable limit.

In another embodiment, the sum of the errors over all electrodes couldbe used to set the convergence criterion.

In another embodiment, using the preferred fitting system as shown inFIG. 15, an image may be adjusted manually by the following steps.

1. Be sure the touch screen monitor 1 is connected to the patienttesting system (PTS) computer and set to be the primary monitor.

2. Adjust the height of touch screen monitor 1 so that the camera ispointed to the center of the touch screen.

3. Open the fitting software on the PTS laptop, change the directory tothe folder containing “Camera Alignment” v1.00, type“runCameraAlignment” and hit “Enter.” Click on the “Camera Position”button. A blank screen will appear on the touch screen.

4. Log in to the clinical fitting system (CFS) and select the“Psychophysics” tab. Log on to PTS and select the “Direct Stimulation”button. Make sure the subject's video processing unit (VPU) is on andconnected to CFS and the subject is wearing the glasses.

5. In the PTS “Direct Stimulation” Screen, stimulate a small group ofelectrodes in the center of the array, and increase the stimulationamplitude and the number of stimulating electrodes until the subjectclearly sees localized bright phosphenes.

6. Adjust the subject seating position and the touch screen monitor 1 inorder to align the camera to the center of the touch screen and about12″ away from the screen. Instruct the subject to look straight aheadwhile keeping their head position as still as possible. Use a chin restif necessary. Generate a phosphene using Direct Stimulation and ask thesubject to point to the location of the phosphene on the touch screenwithout moving their eyes or their head. If the position of thephosphene is not on the touch screen, move the touch screen or adjustthe height of the subject's chair so that the response is on themonitor. Verify that a gray symbol appears on the touch screen at thelocation indicated by the subject.

7. Repeat the stimulation and gather a response 8 times. The touchscreen will display all the outputs from the subject. Click the “Undolast trial” button to remove the last responses from the subject ifnecessary. Click the “Back” button to go back to the main screen andclick the “Exit” button to exit the program. If the touch screen monitor1 or the subject seating is adjusted during this step, repeat the stepto collect 8 responses.

8. The program will calculate the average position of the responses andpresent an alignment target (a white circle) centered at this positionon the touch screen.

9. Log out of PTS. Select the “CamPos” tab in CFS. Instruct the subjectto look straight ahead and to carefully maintain the same head and bodyposition as during the data collection phase. The alignment targetshould appear on the “CamPos” screen. If not, use the right arrow key onthe PTS to increase the size of the alignment target until it appears onthe “CamPos” screen. Adjust the top, bottom, left, and right arrows onthe CFS screen until the alignment target on the touch screen appears atthe center of the “CamPos” screen. Reduce the alignment target size ifnecessary by pressing the left arrow key on the PTS. Click the “save”button on the CFS “CamPos” screen when the alignment target is at thecenter of the screen. This will select and store the section of thecamera image that is aligned with the implant's visual field position onthe subject's VPU. Record the saved camera position in the CRF.

10. Run the Square Localization test again to compare with the baselinedata.

The ellipse from the square localization assessment is also useful insetting up the field of view of the electrode array. The area of theellipse might be used to adjust the zoom of the camera—ie. one might‘zoom out’ for a large ellipse or ‘zoom in’ for a small ellipse. Also,the orientation of the ellipse could be used to adjust the angle or tiltof the camera or field of view. Finally, after adjusting for angle, ifthe ellipse is not a circle, the ellipse could be used to adjust thehorizontal and vertical zoom independently. So, if the ellipse waslonger horizontally, a larger horizontal field of view compared to thevertical field of view could be selected.

One additional advantage of the approach for setting the cameraposition/field of view is that the entire process can be automated.Thus, a patient can sit in front of a screen that presents individualsquare stimuli. The patient then touches the touch screen where he/shebelieves they saw the spot of light. This is repeated for an entire setof locations. The data is then analyzed in real-time (automatically) asdescribed above and automatically downloaded to the VPU to adjust thecamera field of view in real-time. In fact, this can be done during thecourse of the experiment such that data is taken, the field of viewadjusted, and more data is taken to confirm that the alignment wascompleted successfully.

Similarly, the direction of motion software can be used to adjust andconfirm camera/field of view angle with respect to the horizon. Thecamera can be rotated (physically or electronically) in real-time untilthe number of correct responses at zero degrees is maximized.Alternately, the area under the response curve can be integrated and themean value calculated such that the angle which minimizes the mean valueis chosen.

Two spatial vision tests have been developed to supplement GratingVisual Acuity, our primary clinical trial endpoint. These assessmenttools, the Square Localization and Direction of Motion tests in theArgus Training Program, were developed to provide an objective measureof spatial vision in subjects who do not reach the lowest levels of theGrating Acuity scale (2.9 log MAR), but who still receive useful spatialinformation by using the Argus II system. The Square Localization andDirection of Motion tests, device ON and device OFF, were administeredto all US Argus II subjects who had been implanted at least 6 months ago(see below for the sole exception).

During the period in which subjects used misaligned CAPs and testingincluded auditory feedback, two of three subjects showed somesignificant improvement in accuracy. Improvement was very slow,averaging 0.02°/day. Subject S1 showed a total average decrease in errorcentroid distance of 6° during this period. S2's decrease in centroiddistance was not statistically significant, and only fell on average by0.4°. S3 showed a significant decrease of 4°.

When auditory feedback was removed, localization errors significantlyincreased over time for S1 and S2. S3 displayed a nonsignificantreduction in errors over time, but the expected error centroid distancefor the last time point of the linear model of the feedback-ON periodand its confidence interval were lower than any observed distance in thefeedback-OFF period. Final error magnitudes were thus higher at the endof this observation period than before auditory feedback was removed.Comparing linear model expectations at the end of the feedback-OFFperiod with those at the end of the feedback-ON period, centroiddistance significantly increased by 7° for S1, 4° for S2, and 4° for S3.

Over the entire time that subjects used misaligned CAPs, none reportedany problematic percepts. None of the subjects had difficulty usingtheir systems or noticed any discrepancies between their visual perceptsand their other senses. When asked to simultaneously view and hold anilluminated rod, subjects could detect changes in where they localizedthe light when different CAPs were set, but did not readily perceive anysensory discordance.

While little adaptation to misaligned CAPs was observed, CAPs requiredfor proper alignment did fluctuate in all subjects. CAPs that providedoptimal localization accuracy to subjects for a time eventually requiredadjustment to restore accuracy. MANOVA tests found significant effectsof time: p<10⁻⁴ for all subjects. Maximum differences between optimalCAPs for each subject were: 23° for S1, 29° for S2, and 21° for S3.Optimal CAP rates of change pooled across subjects had a median of0.28°/day, mean of 0.39°/day, standard deviation of 0.36°/day, andmaximum rate of 1.8°/day. Certain patterns did appear in how CAPestimates moved over time: optimal CAPs for S2 tended to move up and tothe right over the observed period, and S3's optimal CAPs moved veryconsistently to the right. Changes over time in S3's optimal horizontalCAPs are highlighted in FIG. 11. Other observed shifts were lesspredictable: S1 displayed a weak rightward trend with no apparentvertical trend over time, and S3's vertical shifts only weakly trendeddownward.

FIGS. 12A-12C show examples of subjects' estimated optimal CAPs thatdiffered significantly over time. For each subject, up to 4 pointsindicate the horizontal and vertical limits of optimal CAP positions and1 point indicates the closest observation to the overall average optimalCAP. Arrows on the 4 first points in chronological order have arrowsthat point to the displayed CAP estimate that is next in chronologicalorder.

Visual prostheses with extraocular cameras require calibration tooptimize user hand-camera coordination. Camera input and/or processingcan be changed to improve or degrade pointing accuracy. When users'cameras were not properly configured, those in this study did not seemto fully appreciate the nature of the misalignments. Passive adaptationto misalignments, i.e. without specific instruction and coaching fromsomeone such as a rehabilitation specialist, was possible, but only withvery slow progress. Rates of adaptation seen here were about 4000 timesslower than those for normally sighted subjects wearing prism glasses(Gibson, 1933). S2 did not show significant localization improvementwhile auditory feedback was enabled, in contrast to our two othersubjects. S2 was less diligent in providing precise responses, whichadded more variability to localization data and may have accompaniedpaying less attention to auditory feedback. Both of these factors wouldmake observing significant improvement less likely.

Without consistent auditory feedback on in-lab localization errors,pointing accuracy deteriorated for all of our subjects. Error magnitudesincreased immediately after auditory feedback was removed for S1 and S3,and only gradually increased for S2. This difference could once again beexplained by S2's less diligent approach: if S2 was paying relativelylittle attention to the feedback, one would not expect removing thefeedback to have as great an effect on responses. The gradual yetdistinct increase in S2's errors after feedback was removed, however,does suggest that the feedback worked to maintain the subject'saccuracy, if not improve it. For S1 and S3, the immediate increases inerror magnitude may reflect the feedback acting as a reminder for thesubjects to attend more carefully to how they respond, alongsideproviding information necessary for adaptation.

One might expect daily activities to provide corrective feedback oncamera misalignments, such as reaching for a white mug against a darkbackground, and missing. Unfortunately, subjects in this study did notappear to encounter or register enough of that information to improve ormaintain pointing accuracy. It is possible that rehabilitationspecialists familiar with visual prostheses and camera misalignmentscould teach users to detect and adjust to misalignments in their homeenvironments. Further, a variation of the localization test used in thisstudy that provides more precise feedback and allows users to makemultiple attempts for one target could promote faster adaptation. Theresults of this study are restricted to contexts that do not involvespecific coaching or devices designed to actively train users oncorrecting localization errors.

Lacking the ability to readily and independently adapt to misalignedpercepts, the flexible nature of how prosthetic visual input isintegrated into the perception of egocentric space is a point ofconcern. If users consistently required the same CAP to maintainhand-camera coordination, prosthesis systems would only need to beproperly configured once. If a CAP initially set to maximize pointingaccuracy becomes less suitable over time, however, and users cannotindependently adapt to emergent misalignments, more frequent systemcalibrations will be required.

Some of the variation seen here may stem purely from the alignment andmeasurement processes used in this study; however, the consistent trendsdisplayed over time by S2 and S3 suggest that at least part of thisvariability was intrinsic to the subjects. If variability originatingfrom the subject could be explained by something as simple as how theeye rests in the orbit, prosthesis-integrated eye tracking mechanismsmay be able to adjust CAPs automatically. If more complicated problemsare involved, such as changing alignments of visual and proprioceptivepercepts, more involved rehabilitation training or device programmingmay be needed to maintain optimal hand-camera coordination.

Referring to FIGS. 13 and 14, the glasses 5 may comprise, for example, aframe 11 holding a camera 12, an external coil 14 and a mounting system16 for the external coil 14. The mounting system 16 may also enclose theRF circuitry. In this configuration, the video camera 12 captures livevideo. The video signal is sent to an external Video Processing Unit(VPU) 20 (shown in FIGS. 15 through 18 and discussed below), whichprocesses the video signal and subsequently transforms the processedvideo signal into electrical stimulation patterns or data. Theelectrical stimulation data are then sent to the external coil 14 thatsends both data and power via radio-frequency (RF) telemetry to the coil116 of the retinal stimulation system 1, shown in FIGS. 22 through 25.The coil 116 receives the RF commands which control the applicationspecific integrated circuit (ASIC) which in turn delivers stimulation tothe retina of the subject via a thin film electrode array (TFEA). In oneaspect of an embodiment, light amplitude is recorded by the camera 12.The VPU 20 may use a logarithmic encoding scheme to convert the incominglight amplitudes into the electrical stimulation patterns or data. Theseelectrical stimulation patterns or data may then be passed on to theRetinal Stimulation System 1, which results in the retinal cells beingstimulated via the electrodes in the electrode array 2010 (shown in FIG.22). In one exemplary embodiment, the electrical stimulation patterns ordata being transmitted by the external coil 14 is binary data. Theexternal coil 14 may contain a receiver and transmitter antennae and aradio-frequency (RF) electronics card for communicating with theinternal coil 116.

Referring to FIG. 15, a Fitting System (FS) may be used to configure andoptimize the visual prosthesis apparatus shown in FIG. 22. The FittingSystem is fully described in the related application U.S. applicationSer. No. 11/796,425, filed on Apr. 27, 2007, (Applicant's Docket No.S401-USA) which is incorporated herein by reference in its entirety.

The Fitting System may comprise custom software with a graphical userinterface running on a dedicated laptop computer 10. Within the FittingSystem are modules for performing diagnostic checks of the implant,loading and executing video configuration files, viewing electrodevoltage waveforms, and aiding in conducting psychophysical experiments.A video module can be used to download a video configuration file to theVideo Processing Unit (VPU) 20 discussed above and store it innon-volatile memory to control various aspects of video configuration,e.g. the spatial relationship between the video input and theelectrodes. The software can also load a previously used videoconfiguration file from the VPU 20 for adjustment.

The Fitting System can be connected to the Psychophysical Test System(PTS), located for example on a dedicated laptop 30, in order to runpsychophysical experiments. In psychophysics mode, the Fitting Systemenables individual electrode control, permitting clinicians to constructtest stimuli with control over current amplitude, pulse-width, andfrequency of the stimulation. In addition, the psychophysics moduleallows the clinician to record subject responses. The PTS may include acollection of standard psychophysics experiments developed using forexample MATLAB® (MathWorks™) software and other tools to allow theclinicians to develop customized psychophysics experiment scripts.

Using the psychophysics module, important perceptual parameters such asperceptual threshold, maximum comfort level, and spatial location ofpercepts may be reliably measured. Based on these perceptual parameters,the fitting software enables custom configuration of the transformationbetween video image and spatio-temporal electrode stimulation parametersin an effort to optimize the effectiveness of the visual prosthesis foreach subject.

The Fitting System laptop 10 of FIG. 15 may be connected to the VPU 20using an optically isolated serial connection adapter 40. Because it isoptically isolated, the serial connection adapter 40 assures that noelectric leakage current can flow from the Fitting System laptop 10 inthe even of a fault condition.

As shown in FIG. 15, the following components may be used with theFitting System according to the present disclosure. The Video ProcessingUnit (VPU) 20 for the subject being tested, a Charged Battery 25 for VPU20, the Glasses 5, a Fitting System (FS) Laptop 10, a PsychophysicalTest System (PTS) Laptop 30, a PTS CD (not shown), a CommunicationAdapter (CA) 40, a USB Drive (Security) (not shown), a USB Drive(Transfer) 47, a USB Drive (Video Settings) (not shown), a Patient InputDevice (RF Tablet) 50, a further Patient Input Device (Jog Dial) 55,Glasses Cable 15, CA-VPU Cable 70, FS-CA Cable 45, FS-PTS Cable 46, Four(4) Port USB Hub 47, Mouse 60, Test Array system 80, Archival USB Drive49, an Isolation Transformer (not shown), adapter cables (not shown),and an External Monitor (not shown).

With continued reference to FIG. 15, the external components of theFitting System may be configured as follows. The battery 25 is connectedwith the VPU 20. The PTS Laptop 30 is connected to FS Laptop 10 usingthe FS-PTS Cable 46. The PTS Laptop 30 and FS Laptop 10 are plugged intothe Isolation Transformer (not shown) using the Adapter Cables (notshown). The Isolation Transformer is plugged into the wall outlet. Thefour (4) Port USB Hub 47 is connected to the FS laptop 10 at the USBport. The mouse 60 and the two Patient Input Devices 50 and 55 areconnected to four (4) Port USB Hubs 47. The FS laptop 10 is connected tothe Communication Adapter (CA) 40 using the FS-CA Cable 45. The CA 40 isconnected to the VPU 20 using the CA-VPU Cable 70. The Glasses 5 areconnected to the VPU 20 using the Glasses Cable 15.

In one exemplary embodiment, the Fitting System shown in FIG. 15 may beused to configure system stimulation parameters and video processingstrategies for each subject outfitted with the visual prosthesisapparatus. The fitting application, operating system, laptops 10 and 30,isolation unit, and VPU 20 may be tested, and configuration controlledas a system. The software provides modules for electrode control,allowing an interactive construction of test stimuli with control overamplitude, pulse width, and frequency of the stimulation waveform ofeach electrode in the Retinal stimulation system 1. These parameters arechecked to ensure that maximum charge per phase limits, charge balance,and power limitations are met before the test stimuli are presented tothe subject. Additionally, these parameters may be checked a second timeby the VPU 20's firmware. The Fitting System shown in FIG. 15 may alsoprovide a psychophysics module for administering a series of previouslydetermined test stimuli to record subject's responses. These responsesmay be indicated by a keypad 50 and/or verbally. The psychophysicsmodule may also be used to reliably measure perceptual parameters suchas perceptual threshold, maximum comfort level, and spatial location ofpercepts. These perceptual parameters may be used to custom configurethe transformation between the video image and spatio-temporal electrodestimulation parameters thereby optimizing the effectiveness of thevisual prosthesis for each subject. The Fitting System is fullydescribed in the related application U.S. application Ser. No.11/796,425, filed on Apr. 27, 2007, (Applicant's Docket No. S401-USA)which is incorporated herein by reference in its entirety.

The visual prosthesis apparatus may operate in two modes: i) stand-alonemode and ii) communication mode.

Stand-Alone Mode

Referring to FIG. 16, in the stand-alone mode, the video camera 12, onthe glasses 5, captures a video image that is sent to the VPU 20. TheVPU 20 processes the image from the camera 12 and transforms it intoelectrical stimulation patterns that are transmitted to the externalcoil 14. The external coil 14 sends the electrical stimulation patternsand power via radio-frequency (RF) telemetry to the implanted retinalstimulation system. The internal coil 116 of the retinal stimulationsystem 1 receives the RF commands from the external coil 14 andtransmits them to the electronics package 4 that in turn deliversstimulation to the retina via the electrode array 2. Additionally, theretinal stimulation system 1 may communicate safety and operationalstatus back to the VPU 20 by transmitting RF telemetry from the internalcoil 116 to the external coil 14. The visual prosthesis apparatus may beconfigured to electrically activate the retinal stimulation system 1only when it is powered by the VPU 20 through the external coil 14. Thestand-alone mode may be used for clinical testing and/or at-home use bythe subject.

Communication Mode

The communication mode may be used for diagnostic testing,psychophysical testing, patient fitting, and downloading of stimulationsettings to the VPU 20, before transmitting data from the VPU 20 to theretinal stimulation system 1 as is done for example in the stand-alonemode described above. Referring to FIG. 15, in the communication mode,the VPU 20 is connected to the Fitting System laptop 10 using cables 70,45, and the optically isolated serial connection adapter 40. In thismode, laptop 10 generated stimuli may be presented to the subject, andprogramming parameters may be adjusted and downloaded to the VPU 20. ThePsychophysical Test System (PTS) laptop 30 connected to the FittingSystem laptop 10 may also be utilized to perform more sophisticatedtesting and analysis as fully described in the related application U.S.application Ser. No. 11/796,425, filed on Apr. 27, 2007 which isincorporated herein by reference in its entirety.

In one embodiment, the functionality of the retinal stimulation systemcan also be tested pre-operatively and intra-operatively (i.e. beforeoperation and during operation) by using an external coil 14, withoutthe glasses 5, placed in close proximity to the retinal stimulationsystem 1. The coil 14 may communicate the status of the retinalstimulation system 1 to the VPU 20 that is connected to the FittingSystem laptop 10 as shown in FIG. 15.

As discussed above, the VPU 20 processes the image from the camera 12and transforms the image into electrical stimulation patterns for theretinal stimulation system. Filters such as edge detection filters maybe applied to the electrical stimulation patterns, for example, by theVPU 20 to generate, for example, a stimulation pattern based on filteredvideo data that the VPU 20 turns into stimulation data for the retinalstimulation system. The images may then be reduced in resolution using adownscaling filter. In one exemplary embodiment, the resolution of theimage may be reduced to match the number of electrodes in the electrodearray 2010 of the retinal stimulation system. That is, if the electrodearray has, for example, sixty electrodes, the image may be reduced to asixty channel resolution. After the reduction in resolution, the imageis mapped to stimulation intensity using, for example, a look-up tablethat has been derived from the testing of individual subjects. Then, theVPU 20 transmits the stimulation parameters via forward telemetry to theretinal stimulation system in frames that may employ a cyclic redundancycheck (CRC) error detection scheme.

In one exemplary embodiment, the VPU 20 may be configured to allow thesubject/patient i) to turn the visual prosthesis apparatus on and off,ii) to manually adjust settings, and iii) to provide power and data tothe retinal stimulation system 1. Referring to FIGS. 15 and 16, the VPU20 may comprise a case 800, power button 805 for turning the VPU 20 onand off, setting button 810, zoom buttons 820 for controlling the camera12, connector port 815 for connecting to the Glasses 5, a connector port816 for connecting to the laptop 10 through the connection adapter 40,indicator lights 825 to give visual indication of operating status ofthe system, the rechargeable battery 25 for powering the VPU 20, batterylatch 830 for locking the battery 25 in the case 800, digital circuitboards (not shown), and a speaker (not shown) to provide audible alertsto indicate various operational conditions of the system. Because theVPU 20 is used and operated by a person with minimal or no vision, thebuttons on the VPU 20 may be differently shaped and/or have specialmarkings as shown in FIG. 18 to help the user identify the functionalityof the button without having to look at it. As shown in FIG. 18, thepower button 805 may be a circular shape while the settings button 820may be square shape and the zoom buttons 820 may have special raisedmarkings 830 to also identify each buttons functionality. One skilled inthe art would appreciate that other shapes and markings can be used toidentify the buttons without departing from the spirit and scope of theinvention. For example, the markings can be recessed instead of raised.

In one embodiment, the indicator lights 825 may indicate that the VPU 20is going through system start-up diagnostic testing when the one or moreindicator lights 825 are blinking fast (more than once per second) andare green in color. The indicator lights 825 may indicate that the VPU20 is operating normally when the one or more indicator lights 825 areblinking once per second and are green in color. The indicator lights825 may indicate that the retinal stimulation system 1 has a problemthat was detected by the VPU 20 at start-up diagnostic when the one ormore indicator lights 825 are blinking, for example, once per fiveseconds and are green in color. The indicator lights 825 may indicatethat the video signal from camera 12 is not being received by the VPU 20when the one or more indicator lights 825 are always on and are amber incolor. The indicator lights 825 may indicate that there is a loss ofcommunication between the retinal stimulation system 1 and the externalcoil 14 due to the movement or removal of Glasses 5 while the system isoperational, or if the VPU 20 detects a problem with the retinalstimulation system 1 and shuts off power to the retinal stimulationsystem 1 when the one or more indicator lights 825 are always on and areorange in color. One skilled in the art would appreciate that othercolors and blinking patterns can be used to give visual indication ofthe operating status of the system without departing from the spirit andscope of the invention.

In one embodiment, a single short beep from the speaker (not shown) maybe used to indicate that one of the buttons 825, 805, or 810 have beenpressed. A single beep followed by two more beeps from the speaker (notshown) may be used to indicate that VPU 20 is turned off. Two beeps fromthe speaker (not shown) may be used to indicate that VPU 20 is startingup. Three beeps from the speaker (not shown) may be used to indicatethat an error has occurred and the VPU 20 is about to shut downautomatically. As would be clear to one skilled in the art, differentperiodic beeping may also be used to indicate a low battery voltagewarning, that there is a problem with the video signal, and/or there isa loss of communication between the retinal stimulation system 1 and theexternal coil 14. One skilled in the art would appreciate that othersounds can be used to give audio indication of the operating status ofthe system without departing from the spirit and scope of the invention.For example, the beeps may be replaced by an actual prerecorded voiceindicating the operating status of the system.

In one exemplary embodiment, the VPU 20 is in constant communicationwith the retinal stimulation system through forward and backwardtelemetry. In this document, the forward telemetry refers totransmission from the VPU 20 to the retinal stimulation system 1 and thebackward telemetry refers to transmissions from the Retinal stimulationsystem 1 to the VPU 20. During the initial setup, the VPU 20 maytransmit null frames (containing no stimulation information) until theVPU 20 synchronizes with the Retinal stimulation system 1 via the backtelemetry. In one embodiment, an audio alarm may be used to indicatewhenever the synchronization has been lost.

In order to supply power and data to the Retinal stimulation system 1,the VPU 20 may drive the external coil 14, for example, with a 3 MHzsignal. To protect the subject, the retinal stimulation system 1 maycomprise a failure detection circuit to detect direct current leakageand to notify the VPU 20 through back telemetry so that the visualprosthesis apparatus can be shut down.

The forward telemetry data (transmitted for example at 122.76 kHz) maybe modulated onto the exemplary 3 MHz carrier using Amplitude ShiftKeying (ASK), while the back telemetry data (transmitted for example at3.8 kHz) may be modulated using Frequency Shift Keying (FSK) with, forexample, 442 kHz and 457 kHz. The theoretical bit error rates can becalculated for both the ASK and FSK scheme assuming a ratio of signal tonoise (SNR). The system disclosed in the present disclosure can bereasonably expected to see bit error rates of 10-5 on forward telemetryand 10-3 on back telemetry. These errors may be caught more than 99.998%of the time by both an ASIC hardware telemetry error detection algorithmand the VPU 20's firmware. For the forward telemetry, this is due to thefact that a 16-bit cyclic redundancy check (CRC) is calculated for every1024 bits sent to the ASIC within electronics package 4 of the RetinalStimulation System 1. The ASIC of the Retinal Stimulation System 1verifies this CRC and handles corrupt data by entering a non-stimulating‘safe’ state and reporting that a telemetry error was detected to theVPU 20 via back telemetry. During the ‘safe’ mode, the VPU 20 mayattempt to return the implant to an operating state. This recovery maybe on the order of milliseconds. The back telemetry words are checkedfor a 16-bit header and a single parity bit. For further protectionagainst corrupt data being misread, the back telemetry is only checkedfor header and parity if it is recognized as properly encoded Bi-phaseMark Encoded (BPM) data. If the VPU 20 detects invalid back telemetrydata, the VPU 20 immediately changes mode to a ‘safe’ mode where theRetinal Stimulation System 1 is reset and the VPU 20 only sendsnon-stimulating data frames. Back telemetry errors cannot cause the VPU20 to do anything that would be unsafe.

The response to errors detected in data transmitted by VPU 20 may beginat the ASIC of the Retinal Stimulation System 1. The Retinal StimulationSystem 1 may be constantly checking the headers and CRCs of incomingdata frames. If either the header or CRC check fails, the ASIC of theRetinal Stimulation System 1 may enter a mode called LOSS OF SYNC 950,shown in FIG. 19a . In LOSS OF SYNC mode 950, the Retinal StimulationSystem 1 will no longer produce a stimulation output, even if commandedto do so by the VPU 20. This cessation of stimulation occurs after theend of the stimulation frame in which the LOSS OF SYNC mode 950 isentered, thus avoiding the possibility of unbalanced pulses notcompleting stimulation. If the Retinal Stimulation System 1 remains in aLOSS OF SYNC mode 950 for 1 second or more (for example, caused bysuccessive errors in data transmitted by the VPU 20), the ASIC of theRetinal Stimulation System 1 disconnects the power lines to thestimulation pulse drivers. This eliminates the possibility of anyleakage from the power supply in a prolonged LOSS OF SYNC mode 950. Fromthe LOSS OF SYNC mode 950, the Retinal Stimulation System 1 will notre-enter a stimulating mode until it has been properly initialized withvalid data transmitted by the VPU 20.

In addition, the VPU 20 may also take action when notified of the LOSSOF SYNC mode 950. As soon as the Retinal Stimulation System 1 enters theLOSS OF SYNC mode 950, the Retinal Stimulation System 1 reports thisfact to the VPU 20 through back telemetry. When the VPU 20 detects thatthe Retinal Stimulation System 1 is in LOSS OF SYNC mode 950, the VPU 20may start to send ‘safe’ data frames to the Retinal Stimulation System1. ‘Safe’ data is data in which no stimulation output is programmed andthe power to the stimulation drivers is also programmed to be off. TheVPU 20 will not send data frames to the Retinal Stimulation System 1with stimulation commands until the VPU 20 first receives back telemetryfrom the Retinal Stimulation System 1 indicating that the RetinalStimulation System 1 has exited the LOSS OF SYNC mode 950. After severalunsuccessful retries by the VPU 20 to take the implant out of LOSS OFSYNC mode 950, the VPU 20 will enter a Low Power Mode (described below)in which the implant is only powered for a very short time. In thistime, the VPU 20 checks the status of the implant. If the implantcontinues to report a LOSS OF SYNC mode 950, the VPU 20 turns power offto the Retinal Stimulation System 1 and tries again later. Since thereis no possibility of the implant electronics causing damage when it isnot powered, this mode is considered very safe.

Due to an unwanted electromagnetic interference (EMI) or electrostaticdischarge (ESD) event, the VPU 20 data, specifically the VPU firmwarecode, in RAM can potentially get corrupted and may cause the VPU 20firmware to freeze. As a result, the VPU 20 firmware will stop resettingthe hardware watchdog circuit, which may cause the system to reset. Thiswill cause the watchdog timer to expire causing a system reset in, forexample, less than 2.25 seconds. Upon recovering from the reset, the VPU20 firmware logs the event and shuts itself down. The VPU 20 will notallow system usage after this occurs once. This prevents the VPU 20 codefrom freezing for extended periods of time and hence reduces theprobability of the VPU sending invalid data frames to the implant.

Supplying power to the Retinal stimulation system 1 can be a significantportion of the VPU 20's total power consumption. When the Retinalstimulation system 1 is not within receiving range to receive eitherpower or data from the VPU 20, the power used by the VPU 20 is wasted.

Power delivered to the Retinal stimulation system 1 may be dependent onthe orientation of the coils 14 and 116. The power delivered to theRetinal stimulation system 1 may be controlled, for example, via the VPU20 every 16.6 ms. The Retinal stimulation system 1 may report how muchpower it receives and the VPU 20 may adjust the power supply voltage ofthe RF driver to maintain a required power level on the Retinalstimulation system 1. Two types of power loss may occur: 1) long term(>˜1 second) and 2) short term (<˜1 second). The long term power lossmay be caused, for example, by a subject removing the Glasses 5.

In one exemplary embodiment, the Low Power Mode may be implemented tosave power for the VPU 20. The Low Power Mode may be entered, forexample, anytime the VPU 20 does not receive back telemetry from theRetinal stimulation system 1. Upon entry to the Low Power Mode, the VPU20 turns off power to the Retinal stimulation system 1. After that, andperiodically, the VPU 20 turns power back on to the Retinal stimulationsystem 1 for an amount of time just long enough for the presence of theRetinal stimulation system 1 to be recognized via its back telemetry. Ifthe Retinal stimulation system 1 is not immediately recognized, thecontroller again shuts off power to the Retinal stimulation system 1. Inthis way, the controller ‘polls’ for the passive Retinal stimulationsystem 1 and a significant reduction in power used is seen when theRetinal stimulation system 1 is too far away from its controller device.FIG. 19b depicts an exemplary block diagram 900 of the steps taken whenthe VPU 20 does not receive back telemetry from the Retinal stimulationsystem 1. If the VPU 20 receives back telemetry from the Retinalstimulation system 1 (output “YES” of step 901), the Retinal stimulationsystem 1 may be provided with power and data (step 906). If the VPU 20does not receive back telemetry from the Retinal stimulation system 1(output “NO” of step 901), the power to the Retinal stimulation system 1may be turned off. After some amount of time, power to the Retinalstimulation system 1 may be turned on again for enough time to determineif the Retinal stimulation system 1 is again transmitting back telemetry(step 903). If the Retinal stimulation system 1 is again transmittingback telemetry (step 904), the Retinal stimulation system 1 is providedwith power and data (step 906). If the Retinal stimulation system 1 isnot transmitting back telemetry (step 904), the power to the Retinalstimulation system 1 may again be turned off for a predetermined amountof time (step 905) and the process may be repeated until the Retinalstimulation system 1 is again transmitting back telemetry.

In another exemplary embodiment, the Low Power Mode may be enteredwhenever the subject is not wearing the Glasses 5. In one example, theGlasses 5 may contain a capacitive touch sensor (not shown) to providethe VPU 20 digital information regarding whether or not the Glasses 5are being worn by the subject. In this example, the Low Power Mode maybe entered whenever the capacitive touch sensor detects that the subjectis not wearing the Glasses 5. That is, if the subject removes theGlasses 5, the VPU 20 will shut off power to the external coil 14. Assoon as the Glasses 5 are put back on, the VPU 20 will resume poweringthe external coil 14. FIG. 19c depicts an exemplary block diagram 910 ofthe steps taken when the capacitive touch sensor detects that thesubject is not wearing the Glasses 5. If the subject is wearing Glasses5 (step 911), the Retinal stimulation system 1 is provided with powerand data (step 913). If the subject is not wearing Glasses 5 (step 911),the power to the Retinal stimulation system 1 is turned off (step 912)and the process is repeated until the subject is wearing Glasses 5.

One exemplary embodiment of the VPU 20 is shown in FIG. 20. The VPU 20may comprise: a Power Supply, a Distribution and Monitoring Circuit(PSDM) 1005, a Reset Circuit 1010, a System Main Clock (SMC) source (notshown), a Video Preprocessor Clock (VPC) source (not shown), a DigitalSignal Processor (DSP) 1020, Video Preprocessor Data Interface 1025, aVideo Preprocessor 1075, an I²C Protocol Controller 1030, a ComplexProgrammable Logic device (CPLD) (not shown), a Forward TelemetryController (FTC) 1035, a Back Telemetry Controller (BTC) 1040,Input/Output Ports 1045, Memory Devices like a Parallel Flash Memory(PFM) 1050 and a Serial Flash Memory (SFM) 1055, a Real Time Clock 1060,an RF Voltage and Current Monitoring Circuit (VIMC) (not shown), aspeaker and/or a buzzer (not shown), an RF receiver 1065, and an RFtransmitter 1070.

The Power Supply, Distribution and Monitoring Circuit (PSDM) 1005 mayregulate a variable battery voltage to several stable voltages thatapply to components of the VPU 20. The Power Supply, Distribution, andMonitoring Circuit (PSDM) 1005 may also provide low battery monitoringand depleted battery system cutoff. The Reset Circuit 1010 may havereset inputs 1011 that are able to invoke system level rest. Forexample, the reset inputs 1011 may be from a manual push-button reset, awatchdog timer expiration, and/or firmware based shutdown. The SystemMain Clock (SMC) source is a clock source for DSP 1020 and CPLD. TheVideo Preprocessor Clock (VPC) source is a clock source for the VideoProcessor. The DSP 1020 may act as the central processing unit of theVPU 20. The DSP 1020 may communicate with the rest of the components ofthe VPU 20 through parallel and serial interfaces. The Video Processor1075 may convert the NTSC signal from the camera 12 into a down-scaledresolution digital image format. The Video Processor 1075 may comprise avideo decoder (not shown) for converting the NTSC signal intohigh-resolution digitized image and a video scaler (not shown) forscaling down the high-resolution digitized image from the video decoderto an intermediate digitized image resolution. The video decoder may becomposed of an Analog Input Processing, Chrominance and LuminanceProcessing, and Brightness Contrast and Saturation (BSC) Controlcircuits. The video scaler may be composed of Acquisition control,Pre-scaler, BSC-control, Line Buffer, and Output Interface. The I²CProtocol Controller 1030 may serve as a link between the DSP 1020 andthe I²C bus. The I²C Protocol Controller 1030 may be able to convert theparallel bus interface of the DSP 1020 to the I²C protocol bus or viseversa. The I²C Protocol Controller 1030 may also be connected to theVideo Processor 1075 and the Real Time Clock 1060. The VPDI 1025 maycontain a tri-state machine to shift video data from Video Preprocessor1075 to the DSP 1020. The Forward Telemetry Controller (FTC) 1035 packs1024 bits of forward telemetry data into a forward telemetry frame. TheFTC 1035 retrieves the forward telemetry data from the DSP 1020 andconverts the data from logic level to biphase marked data. The BackTelemetry Controller (BTC) 1040 retrieves the biphase marked data fromthe RF receiver 1065, decodes it, and generates the BFSR and BCLKR forthe DSP 1020. The Input/Output Ports 1045 provide expanded JO functionsto access the CPLD on-chip and off-chip devices. The Parallel FlashMemory (PFM) 1050 may be used to store executable code and the SerialFlash Memory (SFM) 1055 may provide Serial Port Interface (SPI) for datastorage. The VIMC may be used to sample and monitor RF transmitter 1070current and voltage in order to monitor the integrity status of theretinal stimulation system 1.

FIG. 22 shows a perspective view of the implanted portion of thepreferred visual prosthesis. A flexible circuit 2001 includes a flexiblecircuit electrode array 2010 which is mounted by a retinal tack (notshown) or similar means to the epiretinal surface. The flexible circuitelectrode array 2010 is electrically coupled by a flexible circuit cable2012, which pierces the sclera and is electrically coupled to anelectronics package 2014, external to the sclera.

The electronics package 2014 is electrically coupled to a secondaryinductive coil 2016. Preferably the secondary inductive coil 2016 ismade from wound wire. Alternatively, the secondary inductive coil 2016may be made from a flexible circuit polymer sandwich with wire tracesdeposited between layers of flexible circuit polymer. The secondaryinductive coil receives power and data from a primary inductive coil2017, which is external to the body. The electronics package 2014 andsecondary inductive coil 2016 are held together by the molded body 2018.The molded body 18 holds the electronics package 2014 and secondaryinductive coil 16 end to end. The secondary inductive coil 16 is placedaround the electronics package 2014 in the molded body 2018. The moldedbody 2018 holds the secondary inductive coil 2016 and electronicspackage 2014 in the end to end orientation and minimizes the thicknessor height above the sclera of the entire device. The molded body 2018may also include suture tabs 2020. The molded body 2018 narrows to forma strap 2022 which surrounds the sclera and holds the molded body 2018,secondary inductive coil 2016, and electronics package 2014 in place.The molded body 2018, suture tabs 2020, and strap 2022 are preferably anintegrated unit made of silicone elastomer. Silicone elastomer can beformed in a pre-curved shape to match the curvature of a typical sclera.However, silicone remains flexible enough to accommodate implantationand to adapt to variations in the curvature of an individual sclera. Thesecondary inductive coil 2016 and molded body 2018 are preferably ovalshaped. A strap 2022 can better support an oval shaped coil. It shouldbe noted that the entire implant is attached to and supported by thesclera. An eye moves constantly. The eye moves to scan a scene and alsohas a jitter motion to improve acuity. Even though such motion isuseless in the blind, it often continues long after a person has losttheir sight. By placing the device under the rectus muscles with theelectronics package in an area of fatty tissue between the rectusmuscles, eye motion does not cause any flexing which might fatigue, andeventually damage, the device.

FIG. 23 shows a side view of the implanted portion of the visualprosthesis, in particular, emphasizing the fan tail 2024. Whenimplanting the visual prosthesis, it is necessary to pass the strap 2022under the eye muscles to surround the sclera. The secondary inductivecoil 2016 and molded body 2018 must also follow the strap 2022 under thelateral rectus muscle on the side of the sclera. The implanted portionof the visual prosthesis is very delicate. It is easy to tear the moldedbody 2018 or break wires in the secondary inductive coil 2016. In orderto allow the molded body 18 to slide smoothly under the lateral rectusmuscle, the molded body 2018 is shaped in the form of a fan tail 2024 onthe end opposite the electronics package 2014. The strap 2022 furtherincludes a hook 2028 that aids the surgeon in passing the strap underthe rectus muscles.

Referring to FIG. 24, the flexible circuit 1, includes platinumconductors 2094 insulated from each other and the external environmentby a biocompatible dielectric polymer 2096, preferably polyimide. Oneend of the array contains exposed electrode sites that are placed inclose proximity to the retinal surface 2010. The other end contains bondpads 2092 that permit electrical connection to the electronics package2014. The electronics package 2014 is attached to the flexible circuit 1using a flip-chip bumping process, and epoxy underfilled. In theflip-chip bumping process, bumps containing conductive adhesive placedon bond pads 2092, and bumps containing conductive adhesive placed onthe electronic package 2014, are aligned and melted to build aconductive connection between the bond pads 2092 and the electronicpackage 2014. Leads 2076 for the secondary inductive coil 2016 areattached to gold pads 2078 on the ceramic substrate 2060 using thermalcompression bonding, and are then covered in epoxy. The electrode arraycable 2012 is laser welded to the assembly junction and underfilled withepoxy. The junction of the secondary inductive coil 2016, array 2001,and electronic package 2014, are encapsulated with a silicone overmold2090 that connects them together mechanically. When assembled, thehermetic electronics package 2014 sits about 3 mm away from the end ofthe secondary inductive coil.

Since the implant device is implanted just under the conjunctiva it ispossible to irritate or even erode through the conjunctiva. Erodingthrough the conjunctiva leaves the body open to infection. We can doseveral things to lessen the likelihood of conjunctiva irritation orerosion. First, it is important to keep the over all thickness of theimplant to a minimum. Even though it is advantageous to mount both theelectronics package 2014 and the secondary inductive coil 2016 on thelateral side of the sclera, the electronics package 2014 is mountedhigher than, but not covering, the secondary inductive coil 2016. Inother words, the thickness of the secondary inductive coil 2016 andelectronics package should not be cumulative.

It is also advantageous to place protective material between the implantdevice and the conjunctiva. This is particularly important at thescleratomy, where the thin film electrode array cable 2012 penetratesthe sclera. The thin film electrode array cable 2012 must penetrate thesclera through the pars plana, not the retina. The scleratomy is,therefore, the point where the device comes closest to the conjunctiva.The protective material can be provided as a flap attached to theimplant device, or a separate piece placed by the surgeon at the time ofimplantation. Further material over the scleratomy will promote healingand sealing of the scleratomy. Suitable materials include DACRON®,TEFLON®, GORETEX® (ePTFE), TUTOPLAST® (sterilized sclera), MERSILENE®(polyester) or silicone.

Referring to FIG. 25, the package 2014 contains a ceramic substrate2060, with metalized vias 2065 and thin-film metallization 2066. Thepackage 2014 contains a metal case wall 2062 which is connected to theceramic substrate 2060 by braze joint 2061. On the ceramic substrate2060 an underfill 2069 is applied. On the underfill 69 an integratedcircuit chip 2064 is positioned. On the integrated circuit chip 2064 aceramic hybrid substrate 2068 is positioned. On the ceramic hybridsubstrate 2068 passives 2070 are placed. Wirebonds 2067 are leading fromthe ceramic substrate 2060 to the ceramic hybrid substrate 2068. A metallid 2084 is connected to the metal case wall 2062 by laser welded joint2063 whereby the package 2014 is sealed.

Accordingly, what has been shown is an improved visual prosthesis and animproved method for limiting power consumption in a visual prosthesis.While the invention has been described by means of specific embodimentsand applications thereof, it is understood that numerous modificationsand variations could be made thereto by those skilled in the art withoutdeparting from the spirit and scope of the invention. It is therefore tobe understood that within the scope of the claims, the invention may bepracticed otherwise than as specifically described herein.

1. A system for fitting a visual prosthesis comprising: a touch screenmonitor connected to a computer; the computer programmed to perform thesteps: project an image on the touch screen monitor in an actuallocation, provide a prompt for a subject to indicate a perceivedlocation of the image by touching the touch screen monitor, record theperceived location, calculate a difference between the actual locationand the perceived location, and adjust the visual prosthesis based onthe difference.
 2. The system for fitting a visual prosthesis accordingto claim 1, wherein the computer is further programmed to: repeat thesteps of claim 1, at different times; store each difference for each ofthe different times; and refine the adjustment of the visual prosthesisby stored difference values.
 3. The system for fitting a visualprosthesis according to claim 1, wherein the computer is furtherprogrammed to: record a camera sampling position of the visualprosthesis camera; and refine the adjustment of the visual prosthesis bythe camera sampling position.
 4. The system for fitting a visualprosthesis according to claim 1, wherein the computer is furtherprogrammed to: calculate a confidence interval based on error rates; andexclude data with a confidence interval less that a predeterminedminimum.
 5. The system for fitting a visual prosthesis according toclaim 4, wherein the predetermined minimum is 95%.
 6. The system forfitting a visual prosthesis according to claim 4, wherein the confidenceinterval is calculated by t-distributions.
 7. The system for fitting avisual prosthesis according to claim 4, wherein the computer is furtherprogrammed to calculate separate confidence intervals for vertical andhorizontal errors, exclude data with vertical confidence interval ofless than a predetermined amount, and exclude data with a horizontalconfidence interval of less than a predetermined amount.
 8. The systemfor fitting a visual prosthesis according to claim 7, wherein thepredetermined amount is 95%.